Automatic frequency offset compensation apparatus

• US 5,561,665 A
• Filed: 07/31/1995
• Issued: 10/01/1996
• Est. Priority Date: 08/11/1994
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Takahashi, Kenichi, Orihashi, Masayuki, Matsuoka, Akihiko, Ohnishi, Hiroshi
• Primary Examiner(s): Chin, Wellington
• Application Number:
  US08/509,664
• Time in Patent Office: 428 Days
• Field of Search: 370/19, 370/20, 370/105.3, 370/32, 375/261, 375/266, 375/344
• US Class Current: 370/206
• CPC Class Codes: H04L 2027/003 at baseband only
• CPC Class Codes: H04L 2027/0046 Open loops
• CPC Class Codes: H04L 2027/0053 Closed loops
• CPC Class Codes: H04L 27/2332 using a non-coherent carrier

Abstract

An automatic frequency compensation apparatus comprises: a frequency offset prediction portion for predicting a frequency offset of an oscillation signal used for receiving a TDM digital modulation signal from the center frequency of the TDM digital modulation signal using a quadrature baseband signal derived from the TDM digital modulation signal, a vector correlation portion detecting a correlation between the quadrature baseband signal and a predetermined signal, the frequency offset prediction portion predicting when the correlation exceeds a reference value, and a frequency offset compensation portion effects a frequency offset compensation to the quadrature baseband. A convergent coefficient may be decreased with the number of events that the correlation exceeds the reference value. An equalizer may be further provided after the frequency offset compensation portion and the prediction is made using the output of the equalizer. The prediction is effected during the training period or during the training period when the correlation exceeds the reference value. The correlation may be detected using the output of the equalizer and a signal obtained by Judging or digitizing the output of the equalizer.

Claims

1. An automatic frequency compensation apparatus comprising:

first difference vector generation means for continuously generating at least a difference vector provided between first signals in two consecutive first symbol intervals of a quadrature baseband signal per said first symbol period, said quadrature baseband signal being provided through a non-synchronizing quadrature detection of a time-division-multiples digital modulation signal received and for normalizing said difference vector;

second difference vector generation means for generating a predetermined difference vector provided between second signals in two consecutive second symbol intervals of a predetermined time-division multiplex frame synchronizing signal;

vector correlation means responsive to said first and second difference vector generation means for providing a frame vector correlation signal indicative of a correlation between the normalized difference vector and said predetermined difference vector;

comparing means for comparing said frame vector correlation signal with a predetermined value and generating a comparing result signal;

counting means for counting said comparing result signal when said vector correlation is larger than said predetermined value;

frequency offset prediction means responsive to said comparing result signal for predicting a frequency offset of an oscillation signal used for receiving said time-division-multiplex digital modulation signal from a center frequency of said time-division-multiples digital modulation signal in accordance with said normalized difference vector and said predetermined difference vector, renewing the predicted frequency offset using a convergent coefficient when said vector correlation is larger than said predetermined value, and decreasing said convergent coefficient with an increase in an output of said counting means; and

frequency offset compensation means for rotating a phase of said baseband signal in accordance with the predicted frequency offset to output the frequency offset compensated baseband signal.

2. An automatic frequency compensation apparatus as claimed in claim 1, wherein said comparing means further responds to a frame signal of said quadrature baseband signal and compares and generates said comparing result signal once a frame of said frame signal.

3. An automatic frequency compensation apparatus as claimed in claim 1, wherein said comparing means generates said comparing signal irrespective of a frame of said quadrature baseband signal.

4. An automatic frequency compensation apparatus comprising:

frequency offset compensation means for, in accordance with a frequency offset detection signal, rotating a phase of a quadrature baseband signal provided through a non-synchronizing quadrature detection of a time-division-multiples digital modulation signal received;

equalizing means for equalizing the quadrature baseband signal from said frequency offset compensation means to remove a distortion included in the quadrature baseband signal from said frequency offset compensation means and outputting the frequency offset compensated and equalized baseband signal in a normal operation and for performing a training to determine a condition of said equalizing means using a predetermined training signal included in said quadrature baseband signal in a training mode such that said distortion is further removed;

first difference vector generation means for continuously generating a difference vector between signals in two consecutive symbol intervals of said quadrature baseband signal from said equalizing means and normalizing said difference vector;

second difference vector generation means for generating a predetermined difference vector provided between signals in two consecutive symbol intervals of a predetermined time-division multiplex frame synchronizing signal; and

frequency offset prediction means for predicting a frequency offset between an oscillation signal used for receiving said time-division-multiplex digital modulation signal and a center frequency of said time-division-multiplex digital modulation signal in accordance with said normalized difference vector and said predetermined difference vector and generating said frequency offset detection signal in said training mode.

5. An automatic frequency compensation apparatus comprising:

frequency offset compensation means for, in accordance with a frequency offset detection signal, rotating a phase of a quadrature baseband signal provided through a non-synchronizing quadrature detection of a time-division-multiplex digital modulation signal received;

equalizing means for equalizing the quadrature baseband signal from said frequency offset compensation means to remove a distortion included in the quadrature baseband signal from said frequency offset compensation means and outputting the frequency offset compensated and equalized baseband signal in a normal operation mode and for performing a training to determine a condition of said equalizing means using a predetermined training signal included in said quadrature baseband signal in a training mode such that said distortion is further removed;

first difference vector generation means for continuously generating a difference vector between signals in two consecutive symbol intervals of said quadrature baseband signal from said equalizing means and normalizing the difference vector;

second difference vector generation means for generating a predetermined difference vector provided between signals in two consecutive symbol intervals of a predetermined time-division multiplex frame synchronizing signal;

vector correlation means responsive to said first and second difference vector generation means for providing a frame vector correlation signal indicative of a correlation between the normalized difference vector and said predetermined difference vector;

comparing means for comparing said frame vector correlation signal with a predetermined value and generating a comparing result signal; and

frequency offset prediction means responsive to said comparing result signal for predicting a frequency offset between an oscillation signal used for receiving said time-division-multiplex digital modulation signal from a center frequency of said time-division-multiplex digital modulation signal in accordance with said normalized difference vector and said predetermined difference vector, renewing the predicted frequency offset when said vector correlation is larger than said predetermined value in said training mode, and generating said frequency offset detection signal.

6. An automatic frequency compensation apparatus comprising:

frequency offset compensation means for, in accordance with a frequency offset detection signal, rotating a phase of a quadrature baseband signal provided through a non-synchronizing quadrature detection of a time-division-multiplex digital modulation signal received;

equalizing means for equalizing the quadrature baseband signal from said frequency offset compensation means to remove a distortion included in the quadrature baseband signal from said frequency offset compensation means and outputting the frequency offset compensated and equalized baseband signal;

first difference vector generation means for continuously generating a difference vector between signals in two consecutive symbol intervals of said quadrature baseband signal from said equalizing circuit and normalizing the difference vector;

judging means for classifying the equalized quadrature baseband signal into a plurality of digit levels which the equalized quadrature baseband signal may show;

second difference vector generation means for generating a second difference vector provided between signals in two consecutive symbol intervals of an output of said judging means;

vector correlation means responsive to said first and second difference vector generation means for providing a frame vector correlation signal indicative of a correlation between the normalized difference vector and said second difference vector;

comparing means for comparing said frame vector correlation signal with a predetermined value and generating a comparing result signal; and

frequency offset prediction means responsive to said comparing result signal for predicting a frequency offset between an oscillation signal used for receiving said time-division-multiplex digital modulation signal and a center frequency of said time-division-multiplex digital modulation signal in accordance with said normalized difference vector and said predetermined difference vector, renewing the predicted frequency offset when said vector correlation is larger than said predetermined value, and generating said frequency offset detection signal.